1. Field of the Invention
The present invention relates to an adaptive, cost-performance efficient, power-saving apparatus for wireless communication systems, such as but not limited to Bluetooth (BT) [1] receivers, and in particular to a packet-based receiver's decoding algorithm which can detect the presence or absence of the adjacent channel interference (ACI) before the scheduled starting time for receiving a Bluetooth packet [1], and accordingly set the receiver configurations including the filter's pass-band bandwidth (BW), filter's order, the sampling rate or the number of analog-to-digital-converter (ADC) output bits, and the automatic-gain-control (AGC) algorithm to determine the Low Noise Amplifier (LNA) and Variable Gain Amplifier (VGA) settings.
2. Background
A Bluetooth device is required to pass the BT specification [1] including the receiver sensitivity and ACI tests. In order to pass the ACI tests, a high order analog filter which sharply suppresses all out-of-band ACI powers in the frequency domain is required. In addition, the ADC must have sufficient dynamic range and resolution to represent the desired in-band signal plus the residual ACI after the analog filter. However, a high-order analog filter and a high-resolution ADC with a large number of output bits both consume more power and are more expensive to be implemented in the integrated circuit (IC). On the other hand, an analog filter with a narrow pass-band is desirable to suppress more ACI but one with a wide pass-band is desirable to achieve better sensitivities. Therefore, the pass-band BW of an analog filter is usually a design trade-off between more ACI suppressions and better receiver sensitivities. A conventional implementation is to sacrifice some receiver sensitivities in order to meet the ACI specification using an analog filter with minimal required order, and an ADC with a minimal required sampling rate and number of output bits to save the cost and power consumption. Furthermore, with more and more wireless local area network (WLAN) devices (such as 802.11 b/g/n devices [2-4]) also using the same frequency band (around 2.4 to 2.483 GHz), the co-existence of BT and WLAN devices has become a major challenge.
The functional block diagram of a simplified Bluetooth (BT) receiver of prior art is illustrated in FIG. 1. The Radio-Frequency (RF) front-end circuits are detailed in the followings. The antenna 10 is used to receive the radio signal and the low noise amplifier (LNA) 20 amplifies the output of the Antenna 10 according to the low noise amplifier (LNA) Control signal 902 set by the automatic gain control (AGC) 90. The Mixer 30 is used to down-convert the output from low noise amplifier (LNA) 20 into a baseband signal centered at a Low Intermediate Frequency (low-IF) in the frequency domain. The low-IF can be as high a few MHz or as low as 0 Hz (called as zero-IF or direct down-conversion in the present invention) for a typical Bluetooth (BT) receiver. Since the desired signal centers at the IF in the frequency domain, an analog filter 40 that follows is a Band-Pass-filter (BPF) or a Low-Pass-filter (LPF) for IF>0 or IF=0, respectively, to have the same frequency center as the down-converted received signal. The variable gain amplifier (VGA) 50 amplifies the output of analog filter 40 according to the variable gain amplifier (VGA) Control signal 901 set by automatic gain control (AGC) 90. The analog-to-digital converter (ADC) 60 converts the received analog signal into a digital signal (in bits) to be processed by the digital filter 70. The digital filter 70 can suppress the residual adjacent channel interference (ACI) further and the output is sent to the digital decoder 80 for decoding. The automatic gain control (AGC) 90 takes the analog-to-digital converter (ADC) output 601, measures the digital signal power, and determines the low noise amplifier (LNA) 20 and variable gain amplifier (VGA) 50 gain settings using low noise amplifier (LNA) Control 902 and variable gain amplifier (VGA) Control 901 to amplify the received analog signal to achieve an appropriate analog-to-digital converter (ADC) output level to be processed by the digital filter 70.
A certified Bluetooth device is required to pass the Bluetooth (BT) specification [1] including the receiver sensitivity and adjacent channel interference (ACI) tests. Examples of the required adjacent channel interference (ACI) specification for a Bluetooth (BT) receiver with a zero-IF (IF=0 MHz) and a low-IF (IF=3 MHz) are shown in FIG. 2a and FIG. 2b, respectively. In the tables FIG. 2a and FIG. 2b, the first column indicates the center frequency of an interfering signal and the following columns 2-4 specified the threshold carrier to interference power ratio (C/I) in dB for data rate=1, 2, or 3 Mbps, respectively. Specifically in the second row of FIG. 2a, for a −40 dB shown in the second column, the conditions and requirements are: a desired Bluetooth (BT) signal (with its power denoted as “C”) centers at 0 MHz with 1 Mbps data rate has to achieve a bit-error-rate (BER) better than 0.001 against an interfering Bluetooth (BT) signal (with its power denoted as “I”) centers at −8 MHz with a C/I less than or equal to the required C/I threshold −40 dB (C/I≦−40). Details of the absolute value for the desired signal power C are given in the Bluetooth (BT) standards [1]. For most tests in FIG. 2, the interfering signals have much greater powers than those of the desired signal (i.e., C/I<0 in dB). To successfully decode the desired signal, a Bluetooth (BT) receiver usually implements an analog filter 40 and a digital filter 70 in FIG. 1 to suppress any out-of-band interfered signals. In these two examples, an analog LPF is implemented for a Bluetooth (BT) receiver in FIG. 2a and an analog BPF centering at low-IF (IF=3 MHz) is implemented for a Bluetooth (BT) receiver in FIG. 2b. However, according to the adjacent channel interference (ACI) specification, a Bluetooth (BT) receiver has to decode the desired 1 Mbps signal while the interfering signal is 30 dB higher (i.e., C/I=−30) and only 2 MHz away (i.e., adjacent channel interference (ACI) centers at IF+2 MHz) as illustrated in FIG. 2a and FIG. 2b. 
On the other hand, to achieve the best sensitivities in decoding the desired signal, the 3 dB pass-band bandwidth (BW) of the analog filter should be wide enough to allow most of the desired signal power to pass through with the minimal filter distortion. In other words, a narrow pass-band bandwidth (BW) is preferred to pass the adjacent channel interference (ACI) tests by suppressing more adjacent channel interference (ACI) power very close to the center of desired signal but this filter may suppress or distort the desired signal and therefore it is not preferred when better receiver sensitivity could actually be achieved in the absence of adjacent channel interference (ACI). This design dilemma raises a great challenge for the analog filter design: to suppress out-of-band adjacent channel interference (ACI) power as much (and as fast) as possible in the frequency domain, and at the same time to keep the pass-band bandwidth (BW) as wide as possible for the desired signal. Unfortunately, the wider pass-band bandwidth (BW), the smaller adjacent channel interference (ACI) can be suppressed and a higher order adjacent channel interference (ACI) filter could be required to suppress the adjacent channel interference (ACI) as much (or fast) as possible in the frequency domain. This concept is illustrated in FIG. 3 and FIG. 4. In both FIGS. 3 and 4, the filter magnitude response is drawn with its 0 MHz corresponding to the center frequency of the low-IF desired signal. For a low-IF Bluetooth (BT) receiver with a center frequency at 0 MHz in FIG. 2a, the actual band-pass filter center frequency is 0 MHz. For a low-IF Bluetooth (BT) receiver with a center frequency at 3 MHz in FIG. 2b, the actual band-pass filter center frequency is 3 MHz. As shown in FIG. 3, a 2nd order analog filter with an one-sided pass-band 3 dB bandwidth (BW) of 0.7 MHz can suppress around 20 dB adjacent channel interference (ACI) power at IF+2 MHz but an analog filter with an one-sided pass-band 3 dB bandwidth (BW) of 1 MHz requires a 3rd order to do so. It is observed that a 3rd order filter can suppress more adjacent channel interference (ACI) power after IF+2 MHz than that by a 2nd order one. However, as shown in FIG. 2, the most difficult adjacent channel interference (ACI) tests to pass are those when adjacent channel interference (ACI) are close to the frequency center of the desired signal when an analog filter just starts to cut adjacent channel interference (ACI) power but the requirement may jump from 0 dB (C/I=0) to 30 dB (C/I=−30) in 1 MHz when an adjacent channel interference (ACI) changes from IF+1 MHz to IF+2 MHz. The rest of adjacent channel interference (ACI) tests are less difficult to pass when an adjacent channel interference (ACI) has a center frequency far away from the frequency center of the desired signal, when both the 2nd and the 3rd order filters have suppressed 30 dB or more already and the adjacent channel interference (ACI) requirement is either the same or raised at most 10 dB per 1 MHz as shown in FIG. 2.
As a result, the pass-band bandwidth (BW) selection of a Bluetooth (BT) receiver filter is a compromised trade-off between better sensitivity and better adjacent channel interference (ACI) performance and a high order analog filter is commonly implemented. The disadvantages are the high costs in design and implementation due to high complexity, and the high power consumption which is critical to all mobile devices with limited battery capacities. In other words, a fixed compromised filter in a Bluetooth (BT) receiver is neither an optimal design when an adjacent channel interference (ACI) is present, nor will it be an optimal one to have the best sensitivities when an adjacent channel interference (ACI) is absent.
However, the adjacent channel interference (ACI) is not always present and the starting time to receive an expected Bluetooth (BT) packet is known to the Bluetooth (BT) receiver in advance. The observations lead to opportunities for better algorithms and designs proposed in the present invention.
U.S. Pat. No. 8,060,041, issued to Ballantyne et al. entitled “Adaptive receiver for wireless communication device” discloses a high performance receiver and a low power receiver within a wireless communication device (WCD) to reduce power consumption. Upon receiving a signal from a base station, a controller within the WCD detects one or more channel conditions of a radio frequency (RF) environment between the base station and the WCD. The controller selects a high performance receiver to process the received signal when the RF environment is unfavorable and selects a low power receiver to process the received signal when the RF environment is favorable.
However, the above disclosure does not effectively control the N-bit ADCs and the analog filters, which can not save the power significantly. According to the above discussions, it need a method and apparatus to overcome the disadvantage of the prior art.